<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>06元素的层级</title>
    <style>
        body{
            font-size: 50px;
        }
        .box1{
            width: 200px;
            height: 200px;
            background-color: #bfa;
            position: absolute;
            /* 
            对于开启了定位元素，可以通过z-index属性来指定元素的层级
                z-index需要一个整数作为参数，值越大元素的层级越高
                    元素的层级越高越优先显示
                    若不设置，则默认优先显示靠下面的
                    祖先元素层级再高也不会盖住后代元素
            */
        }
        .box2{
            width: 200px;
            height: 200px;
            background-color: rgba(255, 0, 0, .5);
            position: absolute;
            top: 50px;
            left: 50px;
        }
        .box3{
            width: 200px;
            height: 200px;
            background-color: yellow;
            position: absolute;
            top: 100px;
            left: 100px;
        }
        .box4{
            width: 100px;
            height: 100px;
            background-color: orange;
            position: absolute;
        }
    </style>
</head>
<body>
    <div class="box1">1</div>
    <div class="box2">2</div>
    <div class="box3">3
        <div class="box4">4</div>
    </div>
</body>
</html>